1. Field of the Invention
The present invention generally relates to an air directing apparatus for use with appliances such as fuel consuming stoves or fireplaces, and particularly those which operate as a direct venting unit, and more particularly to converting direct venting stoves or fireplaces into natural venting (B vent) units without necessarily modifying any structural part of the stove or fireplace.
2. Description of the Prior Art
Various types of decorative fireplaces and stoves are very popular, typically providing a desired aesthetic effect but often for use as either a secondary heating means in a particular room of a house or as the primary heating means, such as in small cabins or resort homes. Gas fireplaces and stoves continue to gain in popularity. In general, these fireplaces are freestanding as well as built-in units, largely of sheet metal parts and glass, and prefabricated for ready installation in new or existing buildings. Stoves are typically cast metal and freestanding in nature. While the installation of a pre-fabricated fireplace and/or stove can avoid the high expense of installing a masonry fireplace, an issue to address is that there are usually only two operational types of flues to choose from: direct venting units and natural venting units.
The direct venting units are sealed units, meaning that such fireplaces and stoves have sealed combustion chambers that are connected to external venting means for venting the products of combustion (POC""s), while the oxygen needed for the combustion process is provided by supplying outside air from an air source located outside the home. The air is drawn into the combustion chamber generally by the draft created from the hot POC""s rising within the vent stack. These direct venting devices typically bum natural gas or propane gas, and the combustion air introduced and the hot POC""s exhausted are maintained separate from each other, although generally travel through concentric tubes or closely adjacent conduits.
A perceived downside of the direct venting arrangement is that a negative pressure in the POC (exhaust) vent stack will directly affect the drafting or suction of the outside air that is to be introduced into the combustion chamber for burning of the fuel. This means that the hotter the exhaust vent stack gets, the greater the negative pressure will exist inside the vent stack and the faster the hot POC""s will be exhausted up the vent stack. The greater the draft created by the hot gases, the faster the outside combustion air will be sucked into the combustion chamber. However, outside pressure conditions can have a large effect on maintaining balanced operation. For instance, windy conditions can create resistive pressures which the exhaust gas pressure must then overcome, in the extreme, potentially causing a backup of combustion gases, which in turn may prevent combustion air to be adequately sucked into the combustion chamber and lead to an insufficient amount of oxygen to stoichiometrically fuel the fire.
With a natural venting fireplace or stove, openings found on the bottom of the unit provide inlet openings for allowing the air that is needed for combustion to be directly supplied from the ambient room air that surrounds the stove or fireplace. The exhaust gases are vented through a vent stack (e.g., chimney pipe, B-vent type) where the exhausting of hot POC""s is generally carried on independently of the air introduction process, i.e., no xe2x80x9cbalanced fluexe2x80x9d is created. However, with a natural venting operation, there are external factors which might affect this flow. For instance, the home may have other devices which can collectively increase the negative pressure within the house, or a positive pressure gradient may otherwise exist between outside air pressure and the interior air, i.e., a backdraft condition. Those other devices which may increase negative pressure could be a kitchen and bathroom exhaust fan, or a whole-house attic fan.
Favorably, the natural venting stove or fireplace is economically less expensive to purchase and install, because the temperatures at which the POC""s are exhausted are generally much lower than that of a direct venting unit, meaning that an uninsulated or little insulated vent stack could be used.
Ideally, it would be desirable in some instances to combine the benefits of a direct vent unit with those of a natural venting arrangement, and thereby also overcome the difficulties mentioned above. Further, where a natural or B-vent is already present in an existing structure, an adapter to accommodate a direct vent-type unit would also be desirable.
It is a principal object of the invention to provide an apparatus enabling a direct vent appliance, such as a freestanding fireplace or stove, located in a room to operate with a natural vent flue that includes a vent stack for exhausting products of combustion (POC""s) from a combustion chamber of the appliance. The object is met in the present invention with an apparatus comprising a drafthood assembly insertable into the natural vent stack, having an air intake section and an exhaust gas section, each section fluidly isolated from the other, wherein the air intake section introduces air in the room into the direct vent appliance for combustion and the exhaust gas section introduces air in the room into the vent stack to cool POC""s exhausted from the appliance.
It is also a principal object of the invention to provide a drafthood assembly of the foregoing type in the form of an adapter that can be used with an existing direct vent appliance, such as one of a freestanding nature, to convert it for use with an existing natural vent stack.
One embodiment of the drafthood assembly further comprises a hollow cylindrical shell having an interior cavity, with the shell generally concentrically arranged about the exhaust pipe so as to define an annular passageway between the shell and exhaust pipe. A deflector is inserted within the passageway dividing the passageway to form the air intake section and the exhaust gas section, the air intake section being located below the exhaust gas section. In this embodiment, the cylindrical shell includes two sets of longitudinally spaced air inlet openings, one set of openings located above the deflector and the other set located below the deflector, each set of openings conducting ambient air in the room into the respective air intake and exhaust gas sections. Advantageously, air that enters the intake section initially contacts the exhaust pipe to become preheated prior to input within the combustion chamber.
It is another object in a preferred form of the invention to provide an exhaust gas section that has a first part and a second part, whereupon in the first part, the air that enters the drafthood assembly through the upper air inlet opening initially contacts the exhaust pipe to cool the exhaust pipe, thereby cooling POC""s within the exhaust pipe, and whereupon in the second part, the air from the first part continues upwardly therein and mixes with the POC""s prior to entry into the vent stack.
In this preferred form, the hollow exhaust pipe has first and second open ends corresponding to and generally coextensive with the top and bottom ends of the shell, the top end of the shell having a transition assembly secured thereabout. The transition assembly defines the second part of the exhaust section, with the transition assembly forming a mixing area where air mixes with the POC""s exiting the exhaust pipe, thereby cooling the POC""s. The transition assembly in one embodiment comprises a reducer having a top and a bottom end, and an upper exhaust pipe extension having a top and a bottom end. The bottom end of the upper exhaust pipe extension is connected to the top end of the reducer, the reducer spanning the annular passageway and forming a neck for directing air into the second part in the upper exhaust pipe.
A sensor assembly that projects into the first part of the exhaust gas section may further be provided, the sensor assembly measuring the temperature of the POC""s and serving as a fuel cut-off under certain circumstances.